The invention relates to a blade cascade of a continuous-flow machine and a continuous-flow machine with such a blade cascade.
A primary or main flow conveyed through a flow channel is diverted by a lateral pressure gradient parallel to the boundary wall. Since wall-proximal flow layers are diverted more due to their lower speed than wall-distant flow layers, a secondary flow or a channel vortex is formed that overlies the main flow, which results in pressure loss among other things. Such secondary flows occur regularly in blade cascades of continuous-flow machines, such as gas and steam turbines. The blade cascades consist of a plurality of vanes or turbine blades arranged next to each other in a peripheral direction, which are arranged in a rotation-symmetrical flow channel and between each of which a blade channel is formed. The blade channels are each bordered in a radial direction by a radial, external, housing-side side wall and by a radial, inner, seam-side side wall. The side walls are, for example, stationary housing sections, rotor sections, radial inner blade platforms and/or radial external blade cover plates. In a peripheral direction, the blade channels are each bordered by a pressure-side and a suction-side turbine blade wall. To decrease the secondary flows, contouring in the form of elevations and/or depressions is frequently applied to the side walls. Examples of such, particularly non-periphery-symmetrical, side wall contouring are shown in European patent application EP 2 261 462 A1 and in International patent application WO 98/44240 A1.
The object of the invention is to create a blade cascade in a continuous-flow machine with a reduced secondary flow, as well as a continuous-flow machine having improved efficiency.
A blade cascade, according to the invention, of a continuous-flow machine has a plurality of blade channels, which are each bordered in the peripheral direction by a pressure side of a blade and by an opposite suction side of an adjacent blade. In the radial direction, the blade channels are each bordered by two opposite side walls. At least one side wall of the blade channels is furnished with side wall contouring. According to the invention, the side wall contouring is wave-like in the peripheral direction and has at least one elevation, at least one depression, and at least one rib that has a blade profile with a pressure side and with an opposite suction side.
The non-periphery-symmetrical side wall contouring according to the invention causes a reduction of secondary flow vortices and a decrease in deviations of an exit flow angle from the turbine cascade in the side wall-proximal region. The at least one side wall contouring allows for primary pressure gradients, particularly those pressure gradients acting in a peripheral direction, to be favorably influenced, specifically by the at least one blade profile-like rib. In addition, the at least one side wall contouring allows the exit flow angle to be influenced and adjusted by the shaping of at least one elevation running in the primary flow direction, or the main flow direction, and at least one depression running in a primary flow direction, for example, in the respective rear region of the side wall in the vicinity of the side wall in such manner that a subsequent cascade experiences a more favorable entry flow distribution and thereby less flow losses are caused. In addition, it is achieved that an interaction of horseshoe vortices, induced at the leading edge of the blade, with each other and with a channel vortex is prevented or at least reduced.
The at least one elevation and the at least one depression each relate to a non-contoured surface section of the radial inner side wall or radial external side wall. In reference to the inner side wall, the at least one elevation extends from the non-contoured surface section radially outward and thereby represents a channel constriction. The at least one depression extends from the non-contoured surface section radially inward and thus represents a channel expansion. The at least one rib can extend, similar to an elevation, beyond the non-contoured surface section. Also, the at least one rib can extend radially outward from an elevation and thus be “placed on” an elevation. However, the at least one rib can also extend out of a depression radially outward across a non-contoured surface section and thereby be partially arranged in the depression. However, the at least one rib can also extend radially outward from a depression, but not go over the non-contoured surface section and thus be arranged entirely in the depression. If the external side wall is provided with a non-symmetrical side wall contouring, the at least one elevation and the at least one rib basically extend inward and the at least one depression extends in principle radially outward.
Preferably, the side wall contouring is conducted to the downstream side wall edge and thus conducted to the rear axial gap. The downstream side wall edge is hereby also designed in a wave-like manner. In doing so, the at least one elevation, the at least one depression and/or the at least one rib can be conducted individually to the downstream side wall edge. The at least one elevation, the at least one depression and/or the at least one rib begin at the upstream side wall edge so that an upstream side wall edge can also be designed in a wave-like manner. Basically, the side wall contouring can extend beyond the leading edge and trailing edge of the blades.
The at least one elevation and/or the at least one depression can have varying amplitudes to influence the flow in the flow direction. The at least one elevation and/or the at least one depression hereby have in the flow direction various heights and depths. Preferably, the at least one elevation has a height that corresponds to a maximum of 30% of the blade pitch.
Preferably, the pressure side and the suction side of the at least one rib are oriented radially, wherein “radial” also comprises “essentially radial.” “Radial” signifies in particular “steep-walled” with a deviation from the radial direction of up to ±15°. Preferably, the at least one rib has a height that corresponds to a maximum of 30% of the blade pitch.
For exit flow angle control purposes, it is advantageous if the at least one rib is in a range of 40% to 100% of an axial blade width.
To positively influence the horseshoe vortices, it is advantageous if the at least one rib is designed in a range of 0% to 60% of the axial blade width.
Preferably, the side wall contouring has rounded edges. By rounding or chamfering the edges, the formation of vortices that can induce mixing losses is prevented or at least substantially reduced. For example, the at least one rib has a flat rib surface, whose side edges or whose peripheral side edge is/are rounded off. Alternatively, the at least one rib may have rounded or spherically-shaped rib surfaces.
The at least one rib may be constructed in the front and rear, in the flow direction of the continuous-flow machine, in a continuous manner and thus transitioning smoothly into adjacent surface sections. A gentle transition between the rib and a non-contoured side wall section or a section of a periphery-symmetrical side wall contour is hereby created.
To influence the flow, it may also be advantageous if curvature radii of the side wall contouring vary.
A continuous-flow machine according to the invention has at least a blade cascade according to the invention. Due to reduced secondary flows and a simultaneously stronger orientation of the respective exit flow angle of the primary flow in a target direction without sharp edges inducing additional vortices and thus mixture losses, such a continuous-flow machine is characterized by an improved efficiency.
Preferred embodiments of the invention are explained in further detail below using highly simplified schematic illustrations.